1. Field of the Invention
The present invention is related to a tube and particularly to a tube, which is used for making the main frame tube of a bicycle, fabricated by means of the 6-4Ti alloy being cold-rolled as the tube blank with a spiral clearance being welded as a spiral seam such that the tube provides a high strength without being deformed easily.
2. Brief Description of the Related Art
Referring to FIGS. 1 and 2, the tube 10 for making the conventional main frame tube of a bicycle is made of iron or aluminum alloy usually has a seam. The manufacturing process for the tube 10 is in that the flat metal sheet 11 is squeezed by rolls of the rolling press to form a tubular shaped metal sheet 11, and then the tubular shaped metal sheet 11 is welded to form the complete tube 10 with a straight welded seam line 12. The welded seam line 12 is weak in stress such that it is easy for the tube 10 to break at the seam line 12. In order to overcome the deficiency, titanium or titanium alloy is used as the material of the tube 10 instead. Titanium or titanium alloy has good mechanical properties such as rust-prevention, lightness in weight and high strength. However, it is relatively complicated to work with titanium or titanium alloy and titanium is a metal with high elastic restoration. Hence, it is required a special technique regarding titanium to solve the problem in the field of cold working.